This invention relates to manual wheelchairs.
Manual wheelchairs that have typically been sold commercially fall into roughly two different categories: (1) those that are relatively inexpensive and heavy made from welded steel tubular frames and (2) those that are relatively expensive made from lightweight alloys.
The inexpensive variety of wheelchair is typically made from low carbon tubular steel that is welded at many locations, often in or causing the most highly stressed members within the structure. For example, the axle mountings for the large rear wheels of the chair are welded to the frame. Such welds are time-consuming in the manufacturing process, are subject to corrosion in use, and reduce product life. Wheelchairs with welded steel frames are often quite heavy, because such designs typically use telescoping tubular members and fastening systems that add considerable weight to a wheelchair.
The expensive variety of manual wheelchair overcomes some of the deficiencies of the heavier, inexpensive variety with the use of expensive, lightweight alloys. However, those designs do not eliminate costly welds in their manufacturing process.
Welds add cost to either variety of wheelchair since finishing is required for product appearance and market acceptance. For steel wheelchairs, costly chrome plating is the finishing method of choice. For the alloy wheelchairs, polymer-based powder coating is employed.
Welds also add cost to manual wheelchairs since cut-and-weld tubing manufacture requires multiple operations (i.e. cutting, swaging, welding) and components (i.e. a large number of pieces of tubing cut and swaged in different ways).
While some designs (see, e.g. Mattson U.S. Pat. No. 3,814,477) have reduced the number of welds that current conventional designs employ, they do not eliminate them in the highest stress areas of the wheelchair (i.e. the rear-axle mounting). Furthermore, such a wheelchair is not foldable since the rear axle is welded in place between two side frames.